verb - intransitive

origin

Folk etymology: corruption of "watch under".

When the early sailing ships came to the New World with non-seafaring persons onboard, they were encouraged to remain on the top deck as much as possible. Due to seasickness, they often vomited over the side of the deck. When this happened, the crew shouted out "watch under" so that people below with their port holes open could move away from or close the window.